JP2954495B2 - Coated paper - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated paper using a novel coating liquid composition for paper coating, and more particularly, to both of excellent blister resistance and printing strength. The present invention also relates to a coated paper having a large thickness and excellent rigidity.

[0002]

2. Description of the Related Art In recent years, a large amount of pigment-coated paper has been used for printing / publishing or packaging due to demands for color printing and higher-grade packaging paper. Further, in offset printing, with the increase in printing speed, quality requirements regarding the printability of coated paper have become more stringent than ever before. In particular, rigidity and surface strength are required for offset sheet-fed printing presses, and blister resistance and printing strength are required for offset rotary printing presses at the same time. It's getting enough.

[0003] The coated paper is produced by applying a coating liquid mainly composed of a pigment and an adhesive to a paper and drying the coated liquid. In the drying method used for these coated papers, conventionally, heated air is used as a drying heat source, and the heated air is directly brought into contact with a paper sheet to be dried in a drying device to dry. The temperature of the coated paper during drying is almost the same as the wet-bulb temperature of the heated air in the constant-rate drying stage. However, in the case of the heating air, the wet-bulb temperature is low because the proportion of water vapor contained therein is small. Therefore In this drying process, the copolymer latex used as a part of the adhesive for coated paper, can be deposited at the following wet bulb temperature of the heated air, low glass transition temperature copolymerization Generally, a coalesced latex is used.

[0004] Coated paper using a copolymer latex having a low glass transition temperature has a large shrinkage of the coated layer upon drying and is hardly glossy. In addition, it is necessary to perform the treatment at a high pressure, so that the stiffness of the coated paper is reduced and the paper thickness is further reduced. As a method for improving the stiffness of coated paper, there are a method of using a base paper having a large amount of starch adhered as a base paper used in manufacturing a coated paper, and a method of using a large amount as a part of an adhesive in a coating liquid. There is a method of using starch, etc., but none of them has achieved satisfactory effects at present. Also, JP-A-3-64597 and JP-A-Hei-3
In -76896 discloses a low glass transition temperature monomer mixture was emulsion copolymerization in the presence of a high glass transition temperature than the wet bulb temperature of the heated air in drying the copolymer latex,
Changing the glass transition temperature of the core and shell, the coating using the so-called different layer structure latices as part of the adhesive, a method to improve <br/> to so the stiffness is proposed, in this method stiffness of the paper bond strength is not preferable have want reduced to what is improved.

Further, in the conventional drying method using dry air as a heating heat source, since the evaporation of water occurs only from the surface layer of the coated paper, the evaporation of the water causes the water in the coating layer to move to the surface layer. Then, a phenomenon that a part of the adhesive moves to the surface, that is, a so-called binder migration occurs. As a result, the resulting coated paper has a drawback that ink transfer unevenness (motoling) tends to occur when multicolor printing is performed. As a method for suppressing the occurrence of such ink transfer unevenness, a method of lowering the temperature of the drying air and delaying the drying is effective.
Alternatively, it is necessary to extremely slow down the coating speed, and there is a problem in terms of equipment and productivity.

Further, in an offset rotary printing press,
It has long been required to improve both printing strength and blister resistance at the same time.To meet such demands, various types of copolymer latexes used as adhesives for paper coating have been developed. Improvements have been made. In particular, the gel content of the latex, that is, the ratio of the insoluble portion of the film formed by drying the latex to a solvent such as benzene, toluene, and tetrahydrofuran, and the polymer composition of the latex govern print strength and blister resistance. This has been confirmed, and various improvements have been made from this aspect.

For example, Japanese Patent Publication No. 57-10237 and Japanese Patent Publication No. 59
No. -3598 proposes that the latex is adjusted to a specific range of polymer composition and gel content to exhibit excellent performance. Also, JP-A-62-117897 discloses that by mixing a low gel content latex having a specific polymer composition and a high gel content latex in a specific range ratio, printing strength and blister resistance are improved. It is said that both can be improved.

The printing strength of the coated paper is highest when the gel content of the latex used is in the range of 75 to 95% by weight and the glass transition temperature of the copolymer is in the range of -25 to 10 ° C. whereas, blister resistance is low gel content, good good thing as those high glass transition temperature is generally known. Therefore, it is very difficult to improve the printing strength and the blister resistance at the same time, and until now, the printing strength and the blister resistance have been changed by changing the gel content of the latex and the polymer composition within an appropriate range. I had to sacrifice some of my gender and compromise.

[0009]

The conventional technology cannot cope with the recent increase in the speed of a printing press, and produces coated paper having excellent printing strength and blister resistance and high rigidity. At present, there is a strong demand for the appearance of coating liquid compositions that can be used. In view of such a situation, the present inventors have been able to simultaneously improve the printing strength and blister resistance of the current coated paper for printing, and have high rigidity.
The task is to provide

[0010]

According to the present invention, there is provided a coated paper in which a coating liquid composition containing a pigment and an adhesive as a main component is coated on a base paper and dried using water vapor or a gas mainly composed of water vapor. A) an aliphatic conjugated diene-based monomer, b) an ethylenically unsaturated aromatic monomer, c) other copolymerizable with a) and b). Is a copolymer latex obtained by emulsion-copolymerizing a monomer mixture consisting of the following: wherein the glass transition temperature (Tg) of the copolymer constituting the copolymer latex is 30 to 90. It is characterized by using a copolymer latex having a temperature of ° C.

Here, the use of a copolymer latex having a high glass transition temperature as one component in the coating liquid is already known. However, the present inventors, by using a copolymer latex having a high glass transition temperature as an adhesive and combining with a specific drying method, both printing strength and blister resistance during printing are excellent, and the rigidity is high. It has been found that a coating liquid composition capable of producing coated paper can be obtained.

Hereinafter, the present invention will be described in detail.
The glass transition temperature of the copolymer latex of the present invention is 30 to 90.
° C. If the temperature is lower than 30 ° C., sufficient stiffness cannot be given to the coated paper, and the blister resistance decreases. If it exceeds 90 ° C., it is impossible to form a sufficient film even with the drying method of the present invention, and the printing strength is lowered.

The copolymer latex used in the present invention comprises: a) an aliphatic conjugated diene monomer, b) an ethylenically unsaturated aromatic monomer, and c) a copolymerizable with the above a) and b). It is obtained by emulsion copolymerization of a monomer mixture consisting of other monomers. Examples of the aliphatic conjugated diene monomer include 1,3-
Examples thereof include butadiene, 2-chloro-1,3-butadiene, and isoprene, and 1,3-butadiene is generally used.

Examples of the ethylenically unsaturated aromatic monomer include styrene, α-methylstyrene, chlorostyrene and the like. Styrene is generally used. Examples of the other copolymerizable monomers, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate such as (meth) acrylic
Acid esters, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, and maleic acid; and vinyl cyanides such as acrylonitrile. These may be used alone or in combination of two or more. used.

The copolymer latex of the present invention can be produced by a conventionally known method. That is, the method of adding the monomer is not particularly limited, and any of batch addition, divided addition, and continuous addition can be employed. In the emulsion polymerization, conventionally known emulsifiers, polymerization initiators, chain transfer agents, and other auxiliaries can be used.

[0016] As the emulsifier, sulfuric acid ester salts of higher alcohols, alkylbenzenesulfonic acid salts, alkyl diphenyl ether sulfonates, aliphatic sulfonates, aliphatic carboxylic acid salts, sulfuric ester salts of noni on surfactants or the like Or a nonionic surfactant such as a polyethylene glycol alkyl ester type, a polyethylene glycol alkyl ether type, a polyethylene glycol alkyl phenyl ether type, or a mixture of two or more.

As the initiator, a water-soluble initiator such as potassium persulfate, ammonium persulfate and sodium persulfate can be used.

Examples of the chain transfer agent include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, and t-dodecyl mercaptan, tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetramethylthiuram. Examples thereof include thiuram-based compounds such as monosulfide, thioglycolic acid, thiomalic acid and the like, and they can be used alone or as a mixture of two or more. As a method of use, any of batch addition, divided addition, and continuous addition may be employed.

The coating liquid composition of the present invention preferably contains the copolymer latex in an amount of 5 to 25 parts by weight based on 100 parts by weight of the coating pigment. When the amount is less than 5 parts by weight, the printing strength and rigidity of the coated paper obtained are reduced, and
When the amount is more than the weight part, the drying property of the ink becomes slow, and the gloss of the white paper is undesirably reduced.

In order to adjust the viscosity of the coated paper, 1 to 8 parts by weight of commonly used natural adhesives such as starch, modified starch and casein can be used.
As the coating pigment used in the coating liquid composition of the present invention,
One or more of clay, kaolin, calcium carbonate, satin white, aluminum hydroxide, barium sulfate and the like used for ordinary coated paper are used. Further, dispersants, defoamers, release agents and the like can be used.

The blade coater such To coated liquid composition thus prepared is used in the general coated paper production, air knife coater, roll coater, brush coater, size up less coater, a curtain coater, a bar coater , A gravure coater, or another on-machine coater provided with a coating device, coats the base paper in one or more layers.

Further, as the base paper, any base paper of acidic paper making and neutral paper used for general coated paper for printing can be used. The pulp used to make the base paper can be the one used in ordinary paper machines. For example, chemical pulp (KP, SP, AP, etc.), mechanical pulp (S
GP, SCP, RGP, CGP, TMP, CTMP
Etc.) and waste paper pulp (DIP etc.) can be appropriately compounded. The paper machine for making the base paper may be not only a fourdrinier or circular net type paper machine but also a double-sided dewatering type paper machine.

Next, the coated paper of the present invention will be described with reference to FIG. The coating liquid composition applied to the base paper (2) unwound from the unwinder (1) by the coating device (3) is dried by the drying device (4), and is controlled to a predetermined water content and reeled. Winded up in (5).

In order to obtain the coated paper of the present invention, it is necessary that the base paper is coated with the coating composition and then dried by a specific drying method. That is, superheated steam or a gas mainly composed of superheated steam is brought into direct contact with a paper sheet to heat and dry the coating layer, and the steam provided for drying or the gas mainly composed of water vapor and the coating layer are dried. It is necessary to dry the generated water vapor by a drying method comprising heating, regenerating and recycling.

FIG. 2 shows a schematic view of a drying apparatus used in the present invention, and will be described. The high-temperature superheated steam (7) heated by the superheater (6) is sent to the drying device (8), and directly contacts the paper sheet (9) for drying. The paper sheet (9) energized by the high-temperature superheated steam (7) evaporates and gradually evaporates the moisture to obtain a predetermined moisture and exits the drying device (8). The low-temperature steam (10) containing energy, the temperature of which has been lowered, and which contains newly evaporated water, is introduced into the super heater (6) via the blower (11), where it is heated to a predetermined temperature and recovered. The paper sheet (9) is regenerated and provided for drying. At this time, since the amount of the recovered gas corresponding to the water vapor evaporated from the paper sheet increases, the recovered gas is discharged from the discharge port (12) to the outside of the system and constantly circulates a fixed amount.

The gas for heating in the present invention is mainly superheated steam or superheated steam.
It is desirable that the temperature is 75 to 110 ° C. and 20 ° C. or higher than the glass transition temperature (Tg) of the copolymer latex to be used. If the temperature is lower than 75 ° C., the drying temperature is lowered, and the effect of using superheated steam is undesirably reduced. When the temperature difference from the Tg of the copolymer latex of the present invention is less than 20 ° C., it is impossible to form a sufficient film of the copolymer latex of the present invention, and the printing strength is reduced. Wet bulb temperature
If the temperature exceeds 110 ° C., the partial pressure of water vapor in the heating gas becomes high, so that the total pressure of the heating gas becomes too high, and gas leaks from the drying device, and stable operation becomes difficult.

Further, the temperature of the superheated steam of the present invention or a gas mainly composed of superheated steam is preferably in the range of 150 to 500 ° C. If this temperature exceeds 500 ° C., it is difficult to control the degree of drying, and there is a concern that discoloration due to overdrying and deterioration of paper quality may occur. On the other hand, in the case of less than 0.99 ° C. is to decrease the drying rate temperature difference becomes smaller between the heating gas and the paper sheet for the degree of superheat is small, also be chilled <br/> by the peripheral wall of the drying apparatus condensation However, there is a possibility that water droplets may fall on the paper sheet as water droplets, causing paper breakage or quality defects.

According to the drying method of the present invention, the coating layer is rapidly heated to a drying temperature substantially equal to the wet bulb temperature of superheated steam or a gas mainly composed of superheated steam. Thereafter, the coating layer that has reached the drying temperature is successively given the sensible heat of the superheated steam to evaporate the water. Since the water expands and the water evaporates due to the temperature rise inside the coating layer, the volume shrinkage due to drying is small in the coating layer, and the coated paper after drying has low air permeability and excellent blister resistance. It will be. In addition, since the drying temperature is high, it is possible to fuse even a copolymer latex having a high glass transition temperature, the printing strength of the resulting coated paper is improved, and the latex having a high glass transition temperature in the coating layer is further improved. The stiffness is also improved due to the influence of the film.

[0029]

EXAMPLES Next, the present invention will be described in detail with reference to examples. However, the present invention is not limited by these examples. In the examples, the number of parts and% are each unless otherwise specified. Parts by weight and% by weight are shown.

Examples 1 to 11 and Comparative Examples 1 to 4 [Production of copolymer latex] In an autoclave purged with nitrogen, water, each monomer, sodium dodecylbenzenesulfonate (manufactured by NOF Corporation; Name Nulex H), potassium persulfate was charged in the number of copies shown in each column of Table 1,
The polymerization reaction was performed at a reaction temperature of 65 ° C. for 24 hours while stirring the inside. After the above reaction, a silicon-based antifoaming agent is added so as to be about 200 ppm based on the solid content of the latex, the unreacted monomer is removed and concentrated under reduced pressure, and the solid content concentration and pH are adjusted. The latex shown in Table 1 was produced and its properties were measured, and the results were described in the same table.

[0031]

[Table 1]

[Preparation of Paper Coating Composition] The latex shown in Table 1 was used as a synthetic binder, and clay (trade name: Ultracoat, manufactured by Engelhard Co.) and charcoal (trade name: Escalon 2000, manufactured by Sankyo Flour Milling Co., Ltd.) were used as pigments. ), Oxidized starch (trade name: Mermaid M210, manufactured by Shikishima Starch Co., Ltd.) and a dispersant (trade name: Aron T-40, manufactured by Toa Gosei Co., Ltd.) as a natural binder in a composition (dry weight part) shown in Tables 2 and 3. Then, a paper coating liquid composition (color) was prepared.

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

[Preparation of Coated Paper] Each coating liquid composition prepared according to the composition shown in Tables 2 and 3 was coated on a base paper for coated paper (67 g /
m ² ), the coating weight after drying is 14 ± 0.5 per side
/ M ² and coated with the as made and dried to a predetermined moisture by using superheated steam shown in Tables 2 and 3 by the drying device shown in FIG. The same operation was performed on the opposite side of the base paper to obtain a double-side coated paper having a coating weight of 28 g / m ² on both sides. The coated paper thus manufactured is placed in a thermo-hygrostat (20 ° C., 6 ° C.).
(5% RH) for 24 hours, and then subjected to super calendering four times using a test super calender (manufactured by Yuri Roll Co., Ltd.) at a temperature of 50 ° C., a linear pressure of 60 kg / cm, and a speed of 10 m / min. .

The coated paper obtained by the above method was evaluated for the glossiness of white paper, printing strength (dry pick, wet pick), blister resistance and rigidity by the following methods.

Gloss on white paper: Gloss at 75 ° was measured using a gloss meter manufactured by Murakami Color Research Laboratory according to JIS P 8142.

Dry pick: Printing was performed using an ink for picking test (TV = 18 ) manufactured by Tokyo Ink Co., Ltd. using an RI-II type printing test machine.
The degree of picking was measured visually. Results range from 5 (no picking at all) to 1 (worst)
The evaluation was made in five steps, and the average value of five tests was shown.

Wet topic: Using a RI-I type printing test machine, water was supplied onto the test piece with a Molton roll, and immediately thereafter, offset printing ink (trade name: Diatone New GSL Red, TV = 12) manufactured by Sakata Inx Co., Ltd. was used. And the degree of picking was determined with the naked eye. The results were evaluated on a scale of 5 from 5 (no picking at all) to 1 (worst), and indicated as an average value of five tests.

Blister resistance: Printing was performed on both sides of the test piece using an offset printing ink (trade name: TK New Bright 617 black) manufactured by Toyo Ink Co., Ltd. using a RI-II type printing tester. Place the printed test specimen in a constant temperature and humidity chamber (20 ° C, 65
% RH) for 24 hours.
For 2 seconds, indicating the lowest temperature at which blisters occurred.

Stiffness: The stiffness of a paper was measured by its own weight bending method in accordance with JIS P 8143.

Motorling: Using a RI-II type printing test machine, 0.5 cc of offset printing ink (trade name: Diatone New GSL Yellow) manufactured by Sakata Inx was printed. After 30 seconds, offset printing ink (trade name) manufactured by Sakata Inx was used. 0.2 cc (Diatone New GSL Red) was printed and the degree of print unevenness was measured with the naked eye. The results were evaluated on a three-point scale of ○ (object with no unevenness), Δ (object with somewhat unevenness), and × (object with unevenness).

The evaluation results are summarized in Tables 2 and 3. As is clear from Tables 2 and 3, Examples 1 to 1 of the present invention were used.
No. 1 is excellent in both blister resistance and printing strength (dry pick, wet pick), and is also excellent in terms of rigidity.

Examples 12 to 14 and Comparative Examples 5 to 7 The coating liquid compositions prepared according to the compositions shown in Table 4 were used in Example 1.
The coated paper was coated on the base paper for coated paper in the same manner as described above, and dried to a predetermined moisture with a dry gas shown in Table 4 to obtain a double-side coated paper. The coated paper thus produced was subjected to a supercalender treatment in the same manner as in Example 1, and then subjected to a paper quality test.

[0045]

[Table 4]

The results of these evaluations are summarized in Table 4. As is clear from Table 4, Examples 12 to 14 of the present invention are superior in both blister resistance and printing strength (dry pick, wet pick) as compared with Comparative Examples using heated air as a dry gas. It can be seen that the rigidity is also excellent.

[0047]

According to the present invention, a latex having a glass transition temperature of 30 to 90 ° C. is used as a part of the adhesive and has a very high rigidity by being combined with a specific drying method.
Further, it is possible to produce coated paper excellent in both printing strength and blister resistance.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a coater.

FIG. 2 is a diagram showing a drying system for superheated steam.

[Description of Signs] 1 Unwinder 2 Base paper 3 Coating device 4 Drying device 5 Reel 6 Super heater 7 High temperature superheated steam 8 Drying device 9 Paper sheet 10 Low temperature steam 11 Blower 12 Outlet

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoichi Yamazaki 1-30-6 Kamiochiai, Shinjuku-ku, Tokyo Nippon Paper Industries Co., Ltd. (72) Inventor Yasunori Minamisato 1-30-6, Kamiochiai, Shinjuku-ku, Tokyo Nippon Paper Industries Co., Ltd. Product Development Laboratory (58) Field surveyed (Int. Cl. ⁶ , DB name) D21H 19/56-19/60

Claims (2)

(57) [Claims] 1. A coated paper which is coated with a coating liquid composition comprising a pigment and an adhesive as a main component and dried by bringing superheated steam or a gas mainly composed of superheated steam into direct contact with the coating layer. A) an aliphatic conjugated diene monomer, b) an ethylenically unsaturated aromatic monomer, and c) another monomer copolymerizable with the above a) and b). A copolymer latex obtained by emulsion copolymerization of a monomer mixture consisting of a monomer and a copolymer, wherein the copolymer constituting the copolymer latex has a glass transition temperature (Tg) of 30 to 90 ° C. A coated paper which is coated with a coating liquid composition containing the copolymer latex. 2. The coated paper according to claim 1, wherein the temperature of the superheated steam or a gas mainly composed of the superheated steam used for drying the coating liquid composition is 150 to 500 ° C.